The smell of freshly cut grass is an
odour caused by
green leaf volatiles (GLVs) released when it is damaged. Mechanical damage to
grass from activities such as
lawnmowing results in the release of
cis-3-hexenal and other compounds that contribute to a grassy or "green" smell. cis-3-Hexenal has a low
odour detection threshold that humans can perceive at concentrations as low as 0.25 parts per billion.
The GLVs responsible for the smell of freshly cut grass play a role in
plant communication and
plant defence against herbivory, functioning as a distress signal warning other plants of imminent danger and, in some instances, as a way to attract predators of grass-eating insects. For humans, the smell of freshly cut grass is connected through
olfactory memory to past experiences involving the odour and may evoke
nostalgia, eliciting associations with spring or summer.
Chemical composition
When grass is cut or damaged,
lipoxygenase enzymes begin a breakdown of membranes in the plant's cells, producing
linoleic and
linolenic acids. Exposure to oxygen leads to the formation of
cis-3-hexenal, which rapidly breaks down to cis-3-hexenol (leaf alcohol) and (E)-2-hexenal (leaf aldehyde). These
green leaf volatiles (GLVs) are a combination of alcohols,
aldehydes, and
esters. The oxygenated hydrocarbons cause a "green" odour.[1]
The main compound responsible for the smell of freshly cut grass is
cis-3-hexenal. It has a low
odour detection threshold that humans can perceive at concentrations as low as 0.25 parts per billion. The compound is highly unstable and breaks down into (E)-2-hexenal (leaf aldehyde),[2] which may account for why the smell is said to fade rapidly.[3]
The composition of green leaf volatiles produced by cut grasses varies. In lawns, hayfields, and
meadows, other plant species such as
clover may be present. Sweet clover may impart a
haylike or
vanilla-like scent due to the presence of
coumarin.[4]
While grasses release hydrocarbons passively and in response to strong sunlight, when cut or damaged, the emissions may increase by a factor of 180.[5] A second release of volatile organic compounds occurs after grass has been cut. An experiment analysing cut red fescue grass (Festuca rubra) and white clover (Trifolium repens) found prolonged releases of (Z)-3-hexenal, (Z)-3-hexenol, and hexenyl acetate. The emissions also included
acetaldehyde,
acetone,
butanone,
methanol, and possibly
formaldehyde.[6] Highly reactive hydrocarbons released by cut grass combine with gases such as
nitrogen oxides and exacerbate
photochemical smog and urban air pollution by contributing to the formation of aerosols and ozone.[7][8] In cities, lawnmowing can account for 10% of the total hydrocarbon release into the atmosphere.[5]
Biological role
Green leaf volatiles (GLVs) are
volatile organic compounds that play an important role in
plant communication and
plant defence against herbivory. The release of GLVs functions as a distress signal to other plants that danger is imminent. GLVs may also attract the predators of grass-eating insects, with
insect and bird species having been shown to respond to GLV releases by certain injured plants.[9][10]
The smell of freshly cut grass is described as a leafy or "green" scent.[1][16] Positive associations to GLVs released by grasses may be due to their similarity to the GLVs released by edible plants such as vegetables when they are ripe.[17]
The smell of freshly cut grass has been described as "uplifting",[18] and behavioral studies have shown that the smell has a "healing effect on psychological damage caused by stress".[16] Hexanal, which resembles the smell of freshly cut grass, can increase interpersonal trust.[19]
A trademark case before the
Office for Harmonization in the Internal Market addressed an attempt to secure a trademark for the smell of freshly cut grass for use with
tennis balls. An appeals board found that "the smell of freshly cut grass is a distinct smell which everyone immediately recognizes from experience. For many, the scent or fragrance of freshly cut grass reminds them of spring or summer, manicured lawns or playing fields, or other such pleasant experiences."[20]
Happiness in childhood may have a bearing on the subjective experience of the smell. In one study, people born before 1960 recalled a happy childhood when describing the smell of freshly cut grass, while those born after 1960 described unhappy childhoods. Subjects born earlier had pride in the responsibility of cutting grass while those born later associated the smell with chores.[21]
The chemicals responsible for the smell of freshly cut grass are used as
aroma compounds by the
perfume industry.
Hexanal and related compounds are used by the food industry in recreating fruit and vegetable flavours. The yearly production of
cis-3-Hexen-1-ol is about 30 tonnes. The compound, which has the smell of freshly cut grass, is naturally present in tomatoes, kiwifruit, olive oil, and green tea.[26]
^Verbeek, Caro; van Campen, Cretien (July 2013). "Inhaling Memories: Smell and Taste Memories in Art, Science, and Practice". The Senses and Society. 8 (2): 133–148.
doi:
10.2752/174589313X13589681980696.
S2CID193023455.
^Stevenson, Tom (1998). Christie's World Encyclopedia of Champagne & Sparkling Wine. Absolute Press. p. 137.
ISBN978-1-899791-98-9.
^Newcomb, R.D.; McRae, J.; Ingram, J. (2010). "Genetic variation in taste and odour perception: an emerging science to guide new product development". Consumer-Driven Innovation in Food and Personal Care Products: 570–596.
doi:
10.1533/9781845699970.5.570.
ISBN9781845695675.